The present invention relates to a gas insulated electrical apparatus and, more particularly, to a gas insulated electrical apparatus with an arrangement for a prevention of reduction in dielectric strength of the apparatus even in the state whereby a conductive particle is mixed into the gas insulated electrical apparatus.
In many cases, gas insulated electrical apparatuses are used as an arrangement in which a high voltage structure member as a current supplying conductor is arranged in a metal pipe in which a negative gas, for instance, SF.sub.6 gas, is sealingly enclosed. In the event that a conductive particle is mixed into this apparatus and drops and is deposited onto the bottom portion of the pipe, this conductive particle rises from the inner surface of the pipe in dependence upon an electric field of the inside of the pipe and floats in the gas space. The dielectric strength of the gas space remarkably deteriorates due to this floating conductive particle. To assure insulation reliability of the apparatus, it is necessary to provide an arrangement which prevents an influence of such a conductive particle.
To solve this problem, in, for example, Japanese Patent Application Laid-Open No. 136811/80, an apparatus is proposed which includes an arrangement in which, by forming an insulation layer having a high dielectric constant on the inner surface of a pipe, a strong electrostatic attracting force capable of overcoming an electrostatic floating force that acts on a conductive particle acts between the conductive particle and the bottom portion of the pipe due to a voltage which is applied to the apparatus and suppresses the floating motion of the conductive particle. In this case, it is necessary to form the insulation layer using high dielectric material whose specific inductive capacity is larger than a predetermined value. Conventionally, a specific inductive capacity of an organic high molecular compound cannot be more than six. Although a specific inductive capacity of an inorganic compound such as sintered barium titanate can be thousands, the sintered barium titanate or the like is fragile and cannot be machined. Furthermore, it is difficult to fit the sintered barium titanate to an inner surface of a pipe having a round surface.
On the other hand, it is necessary to increase the electrostatic attracting force to attract a conductive particle on the insulation layer and to further improve the insulation performance of the apparatus.